One representative ceramic electronic component is a multilayer ceramic capacitor having a structure as shown in FIG. 5 for example.
This multilayer ceramic capacitor is, as shown in FIG. 5, structured such that a stack of ceramic layers (a ceramic body) 60 having a plurality of internal electrodes 52 (52a, 52b) stacked in layers with a ceramic layer 51 that is a dielectric layer interposed has opposite end surfaces 53a and 53b provided with an external electrode 54 (54a, 54b) electrically connected to internal electrode 52 (52a, 52b).
When such a multilayer ceramic capacitor is produced, external electrode 54 (54a, 54b) is formed generally by a method of applying and firing a conductive paste on the opposite end surfaces of the stack of ceramic layers (or the ceramic body).
As such a conductive paste used to form the external electrode, there has been proposed a conductive paste for example containing at least metallic powder and a BaO—SrO—ZnO—B2O3—SiO2-based glass frit, the glass frit, as converted into oxide, containing 10-50% by weight of BaO, 5-40% by weight of SrO, 10-30% by weight of ZnO, 15-30% by weight of B2O3 and 3-20% by weight of SiO2, with 0.5-10% by weight of the glass frit contained relative to 100% by weight of the metallic powder (see PTD 1).
It is said that the external electrode formed of this conductive paste has the glass frit less easily permeating through the ceramic that configures the stack of ceramic layers when fired. It is believed that this is because the glass frit used in the conductive paste of PTD 1 has a large content of BaO and SrO and is thus less reactive to the ceramic body.
Furthermore, as another conductive paste, a conductive paste has been proposed that contains at least one conductive powder selected from copper powder, nickel powder, copper-nickel-alloys powder and their mixture, and a glass frit free of lead, bismuth and cadmium and having a softening point of 530 to 650° C. and a coefficient of thermal expansion of 9.0 to 11.5 ppm/° C. with the conductive powder and glass frit dispersed in an organic medium (see PTD 2).
And it is said that the conductive paste of PTD 2 can provide an external electrode having high density and presenting excellent adhesion to the ceramic body.
However, the conductive paste of PTD 1 has a small amount of SiO2 used in the glass frit, and accordingly, the glass contained in the external electrode formed using the conductive paste of PTD 1 is easily dissolved in a plating liquid and in the step of plating the external electrode the plating liquid infiltrates into the external electrode, the ceramic body and the like, resulting in the multilayer ceramic electronic component having disadvantageously reduced mechanical strength.
Furthermore, the conductive paste of PTD 2 also has a problem similar to the above problem described for the conductive paste of PTD 1.
PTD 1: Japanese Patent Laying-Open No. 2003-077336
PTD 2: Japanese Patent Laying-Open No. 2004-228075